Most conventional polymers derived from petroleum resources such as polyethylene terephthalate (PET), nylon, polyolefin and polyvinyl chloride (PVC) resins, have been used for materials for a wide range of applications such as packaging materials. However, these polymers are resistant to biodegradation and related to environmental issues like carbon dioxide gas, which causes the global warming on the waste treatment processes. In addition, there have been wide studies on the use of biomass-based resins including polylactic acid following the depletion of petroleum resources.
However, as polylactic acid derived from plants is lower in heat resistance and mechanical properties than petroleum-based resins, there have been limitations of the plastic applications. Particularly, attempts have been made to use polylactic acid resins as packaging materials such as packaging films, but they have failed due to the poor flexibility of polylactic acid resins.
In order to overcome the problems of polylactic acid resins, it has been suggested that low-molecular weight flexibilizers or plasticizers be added to polylactic acid resins, or plasticizers produced by addition polymerization of polyether-based or aliphatic polyester-based polyol be applied to the polylactic acid resins.
However, there is little improvement of flexibility in most of the packaging films comprising polylactic acid resins which are produced according to these methods. Furthermore, the packaging films exhibit poor stability as the plasticizers bleed out over time, and have the disadvantages of an increase in haze together with a decrease in low transparency. In most cases of conventional methods, an improvement in flexibility results from a great decrease in mechanical properties, workability, dimensional stability, and anti-blocking properties, and thus it is unsuitable for use in packaging films. Therefore, a polylactic acid resin that allows the production of packaging films with optimized flexibility is required.
Further, another problem of polylactic acid resins resides in poor heat resistance. When exposed to a high temperature, polylactic acid resins or films made thereof may undergo degradation by depolymerization.
Accordingly, there is a continuous demand for a polylactic acid resin film that has improved flexibility and exhibits excellent properties including mechanical properties, transparency, heat resistance, anti-blocking property, workability, and anti-bleed-out properties.